1. Field of the Invention
This invention relates to new, liquid bis-oxazolidines, to mixtures containing these oxazolidines, to a process for their production and to their use as hardeners for plastics precursors containing isocyanate groups.
2. Description of the Prior Art
Compounds containing oxazolidine structural units I ##STR3## which will be referred to hereinafter simply as oxazolidines, have the property of splitting back into the starting components, hydroxyamine and carbonyl compound, for example under the effect of atmospheric moisture.
Accordingly, compounds such as these are potential reactants for polymer precursors containing isocyanate groups, in particular organic polyisocyanates or isocyanate prepolymers. DE-PS 2,446,438 describes oxazolidines containing urethane groups which are free from ester groups and, accordingly, show increased stability to hydrolysis, particularly in the alkaline range. These oxazolidines may be mixed with isocyanate prepolymers based on aliphatic diisocyanates to form one-component formulations which shown high stability in storage and which cure in the presence of moisture to form crosslinked coatings.
Oxazolidines based on bis-hydroxyamines and aldehydes may be easily produced and show a balanced ratio of reactivity and stability in storage.
However, the aldehyde-based oxazolidines described in DE-PS 2,446,438, particularly those used in the examples, are still attended by certain disadvantages, namely:
The oxazolidines mentioned have a pronounced tendency to change into a crystalline state during storage which presents considerable problems when it comes to storage, transport and application. Accordingly, either solvents have to be added, which is undesirable on ecological and economic grounds, or the products have to be stored above room temperature, i.e. in heated rooms, which is also a considerable practical disadvantage. PA1 The oxazolidines mentioned have viscosities of more than 15,000 mPa.s at room temperature, such that reactive diluents and/or volatile solvents often have to be used during their production and during processing of the coating compositions produced therefrom. PA1 The known oxazolidines mentioned contain readily volatile aldehydes which can lead to unwelcome emissions during the application of corresponding formulations on account of their high volatility and their pungent odor. PA1 a) bis-oxazolidines corresponding to formula (II) above and PA1 b) 0.03 to 0.3 moles per mole of component (a), of compounds corresponding to formula (III) ##STR5## wherein R represents a saturated, branched, aliphatic hydrocarbon radical containing 5 to 8 carbon atoms. PA1 i) reacting diethanolamine with 1.01 to 1.5 moles, per mole of diethanolamine, of an aldehyde corresponding to formula (IV) ##STR6## at 60.degree. to 160.degree. C., optionally in the presence of an entraining agent, to form a monohydroxyoxazolidine corresponding to formula (III) and removing the excess aldehyde and entraining agent by distillation after the reaction, and PA1 (ii) reacting 1,6-diisocyanatohexane with 2.03 to 2.3 moles, per mole of 1,6-diisocyanatohexane, of the oxazolidine corresponding to formula (III) and obtained in the first step until no more isocyanate groups can be detected in the reaction mixture.
It has now surprisingly been found that the bis-oxazolidines containing urethane groups according to the invention and mixtures containing these oxazolidines, which are both described in detail hereinafter, are not attended by any of these disadvantages. The bis-oxazolidines and oxazolidine mixtures according to the present invention are low viscosity, solvent-free products which may be processed without a pungent odor emission, show no tendency towards crystallization, even after storage at low temperatures, and are eminently suitable as hardeners for polymer precursors containing isocyanate groups.